The present invention relates to a memory cell array. More particularly, to a memory cell array in a semiconductor memory device wherein a width of a select line having a source select line SSL and a drain select line DSL is reduced.
Generally, a semiconductor memory device includes a volatile memory device where data are extinguished when a power is not supplied and a non-volatile memory device where data are maintained though the power is not supplied. The volatile memory device has a dynamic random access memory (DRAM) and a static random access memory (SRAM).
The non-volatile memory device includes an electrically erasable and programmable ROM (EEPROM) where data may be inputted or outputted electrically and a flash memory device, etc.
Especially, the flash memory device is a device improved compared to the EEPROM, and controls electrically an input/output of data by using Fowler-Nordheim tunneling (F-N tunneling) phenomenon or a hot electron injection phenomenon.
In addition, the flash memory device is divided into a NAND flash memory and a NOR flash memory.
The NAND flash memory includes a cell string where memory cell transistors are connected in series one another and with word lines. The word lines are connected in parallel between a bit line and a common source line.
In the NOR flash memory, each of memory cell transistors is connected in parallel between a bit line and a common source line.
The NOR flash memory has an excellent fast-operation characteristic because data are inputted/outputted in an unit of a memory cell transistor. However, the characteristic is not good in view of degree of integration. Whereas, the NAND flash memory has an excellent integration characteristic because data are inputted/outputted in an unit of a word line.
The NAND flash memory has a select line included in a memory cell array, wherein select transistors are connected in series with the select line. Here, the select line is formed at both terminals of a cell string where memory cell transistors are connected in series to one another. Additionally, the select line selects the cell string for inputting/outputting data or interrupts a cell string that has not been selected.